CENOZOIC EPISODIC VOLCANISM AND CONTINENTAL RIFTING IN NORTHEAST CHINA AND POSSIBLE LINK TO JAPAN SEA DEVELOPMENT AS REVEALED FROM K-AR GEOCHRONOLOGY

Abstract

Cenozoic volcanic rocks in northeast China comprise part of the volcanic belt of the western circum-Pacific rim and represent one of the presently active tectono-magmatic regions of the world. Over 590 volcanoes with erupted basalts covering an area of ∼50,000km2 are exposed in the Songliao graben and particularly on its flanks. K–Ar dating of the volcanic rocks sampled from a selection of eruption sites over the region reveals that the volcanism occurred episodically through the entire Cenozoic corresponding to the tectono-magmatic interactions particularly between the India, Eurasia and Pacific Plates. The volcanism initiated in the Songliao graben in late Cretaceous (∼86Ma) and migrated flankward since ∼28Ma. The magmatic propagation shows three major stages intimately associated with the evolution of Japan Sea and related to the geodynamic forcing of the India–Eurasia collision. Prior to Japan Sea rifting, volcanic eruptions were restricted to the Songliao basin. During Japan Sea opening, volcanism migrated into the lateral belts. After cessation of Japan Sea opening at ∼15Ma, volcanism with greatest intensity occurred on both flanks particularly along the Yi–Yi fault system around 14–13Ma and subsequently the Fu–Mi fault between 11 and 7Ma. Continuing this trend of migration, eruptions scattered further away from the Songliao basin in the last 4.5Ma. We suggest that the Cenozoic volcanic belt in northeast China and the Japan Sea backarc basin are competitive parts in the eastern-marginal magmatic system of the Eurasian Plate. The early stage of the volcanism in the Songliao basin may have resulted from mantle upwelling beneath the Songliao–Bohai basin belt. Rifting of the NE faults and relatively weak intensity of volcanism in northeast China during Japan Sea opening could be attributable to the lithospheric breakup in the Japan Sea and spreading of Japan Sea. The subsequent strong volcanism in northeast China after cessation of the Japan Sea opening implicates the easiest pathway for the melts of the magmatic system in the plate margin. The diversified volcanism in scattered localities during the Quaternary may indicate localized melting processes or notable modifications in smaller sized individual domains and possibly, a magmatically waning phase of the limited source in eastern China.